/Engine/Source/Runtime/Engine/Classes/GameFramework/GameModeBase.h
If login is successful, returns a new PlayerController to associate with this player. Login fails if ErrorMessage string is set.
a new player controller for the logged in player, NULL if login failed for any reason
virtual [APlayerController](API\Runtime\Engine\GameFramework\APlayerController) * Login ( [UPlayer](API\Runtime\Engine\Engine\UPlayer) * NewPlayer, ENetRole InRemoteRole, const [FString](API\Runtime\Core\Containers\FString) & Portal, const [FString](API\Runtime\Core\Containers\FString) & Options, const [FUniqueNetIdRepl](API\Runtime\Engine\GameFramework\FUniqueNetIdRepl) & UniqueId, [FString](API\Runtime\Core\Containers\FString) & ErrorMessage )